1. Field of the Invention
This invention relates to a light modulation element for changing the position of a needle by an electrostatic stress for executing light modulation, an array-type light modulation element, a drive method thereof, and a flat-panel display unit.
2. Description of the Related Art
A light modulation element is available for controlling the amplitude (strength), phase, travel direction, etc., of incident light for processing and displaying an image, pattern data, etc. One of the light modulation elements is a liquid crystal light modulation element using the electro-optic effect of liquid crystal. The liquid crystal light modulation element preferably is used with a liquid crystal display of a thin flat-panel display unit. The liquid crystal display has a structure wherein oriented liquid crystal is entered and sealed between substrates forming a pair of conductive transparent films and sandwiched between orthogonal deflecting plates. The liquid crystal display produces display by applying a voltage to the conductive transparent film for orienting the liquid crystal molecules in the long axis direction perpendicular to the substrate and changing the transmission factor of light from a backlight.
By the way, in the liquid crystal display, light from the backlight is allowed to pass through multiple layers of the deflecting plates, transparent electrodes, and color filter, thus the light use efficiency lowers. The high-grade liquid crystal display requires TFTs and liquid crystal must be sealed between two substrates and be oriented, thus it is difficult to provide a large screen. This is a disadvantage of the liquid crystal display. Further, since light is allowed to pass through between the oriented liquid crystal molecules, the viewing angle becomes narrow. This is another disadvantage of the liquid crystal display.
To solve such disadvantages, an electrostatically driven light modulation element is proposed. This light modulation element comprises an alternating pattern of a first shield section having a plurality of drive electrodes insulated from each other arranged in a predetermined spacing in a predetermined direction and a second shield section movable with positive and negative charges electrostatically induced, the first and second shield sections being placed on a transparent substrate. The voltage applied to the drive electrode is changed, whereby the relative position between the first and second shield sections is changed by an electrostatic stress between the first and second shield sections, thereby changing the transmission factor of light passing through therebetween for executing light modulation.
According to the electrostatically driven light modulation element, light from the light source is allowed to pass through only the transparent substrate, so that the light use efficiency can be raised and the light modulation elements can be easily put into an array by photolithography and etching and liquid crystal need not be poured or oriented, thus the manufacturing costs can be reduced and a large area can be easily provided.
However, in the electrostatically driven light modulation element in the related art described above, the displacement relationship between the applied voltage and the relative position between the first and second shield sections shows a hysteresis characteristic, thus generally the applied voltage to the drive electrode is changed binarily. Therefore, the drive method becomes so-called simple matrix drive for connecting scan signal electrodes and image signal electrodes to the first shield section and the second shield section, scanning the scan signal electrodes in sequence, and applying signal voltages corresponding to the scanned scan signal electrodes to the image signal electrodes. However, in the simple matrix drive, the condition of the voltages applied to the scan signal electrodes and the image signal electrodes depends on the hysteresis characteristic and is restricted. To enhance the image quality of contrast, etc., it becomes necessary to optimize the element structure and fit the hysteresis characteristic to the drive condition.
For binary simple matrix drive, a method of dividing one image display into fields, scanning, and changing the display time for providing gradation is possible as means for providing gradation. In this case, even in a drive method of weighting scan intervals in the fields for decreasing the number of scan times, the write scan time becomes short and a restriction is placed on design so that the light modulation element responds sufficiently to it.
In contrast, some liquid crystal displays adopt active matrix drive of adding active elements (TFT, etc.,) to intersection parts of an XY matrix and applying voltage to liquid crystal through the active elements. In the active matrix drive, scan voltage is applied to scan signal electrodes in sequence and the TFTs connected thereto are turned on in unison. At the same time, a signal is applied from image signal electrodes and charges are accumulated in capacitance of each pixel through the TFTs. At the termination of scanning one line, the TFTs are turned off and the charges accumulated in the pixel capacitance are retained (memorized) intact. According to the active matrix drive, applied voltage can be set as desired in a wide range and comparatively fast response speed and high contrast can be provided, so that high picture quality can also be provided particularly in a moving picture.
Thus, development of light modulation elements having a memory property while inheriting the advantages, thereby enabling active matrix drive is also demanded in the electrostatically driven light modulation elements.
It is therefore an object of the invention to provide a light modulation element provided with a memory property according to a simple/and low-cost configuration for enabling matrix drive capable of performing the operation at high speed and producing high-contrast display, an array-type light modulation element, a drive method thereof, and a flat-panel display unit.
To the end, in this invention, there is provided a light modulation element for performing electromechanical operation of generating a first electromechanical force for a needle for displacing the needle, thereby changing a transmission factor of light, the light modulation element comprising drive means for generating or canceling a second electromechanical force for the needle in a direction different from that of the first electromechanical force and holding or canceling the displacement state of the needle.
In the light modulation element, the light modulation operation is performed by the first electromechanical force and the displacement state of the needle can be held or canceled in response to the second electromechanical force generated by the drive means. Thus, a memory property can be provided for the light transmission factor of the light modulation element and the element structure enabling active matrix drive can be provided.
In the light modulation element in this invention, the electromechanical force is an electrostatic force produced by an electric field.
In the light modulation element, an electrostatic force acts because of the potential difference caused by voltage application and the first, second electromechanical force can be driven by the electrostatic force.
In the light modulation element in this invention, the electromechanical force is an electromagnetic force.
According to the light modulation element, first, second electro-mechanical force can be driven by the electromagnetic force generated by an electromagnet, etc.
In the light modulation element in this invention, the electro-mechanical force is a force produced by an electrostrictive strain effect.
According to the configuration, the first, second electromechanical force can be driven by the electrostrictive strain force of a piezo-element, etc.
In the light modulation element in this invention, the directions of the first and second electromechanical forces are substantially orthogonal to each other.
According to the configuration, the interference between the electromechanical forces lessens and accurate drive control is enabled.
In the light modulation element in this invention, the direction of the first electromechanical force is substantially horizontal and the direction of the second electromechanical force is substantially vertical.
In the light modulation element, the needle is moved substantially in the horizontal direction by the first electromechanical force, whereby light modulation can be executed and the needle is sucked or attracted substantially in the vertical direction for holding the displacement state of the needle or the electromechanical force is canceled and the displacement state can be canceled.
In the light modulation element in this invention, the direction of the first electromechanical force is substantially vertical and the direction of the second electromechanical force is substantially horizontal.
In the light modulation element, the needle is moved substantially in the vertical direction by the first electromechanical force, whereby light modulation can be executed and the needle is sucked or attracted substantially in the horizontal direction for holding the displacement state of the needle or the electromechanical force is canceled and the displacement state can be canceled.
The light modulation element in this invention comprises a needle being partially supported on the side of a substrate and having electric conductivity and a first fixed electrode and a second fixed electrode being placed facing the needle, wherein the needle is displaced substantially horizontally with respect to the substrate based on a potential difference caused by voltage application to the first fixed electrode and the needle, thereby changing the light transmission factor and wherein the displacement state of the needle is held or canceled by voltage application to the second fixed electrode and the needle.
In the light modulation element, the needle can be moved substantially in the horizontal direction in response to the potential difference by the electrostatic force in the horizontal direction generated by voltage application to the first fixed electrode and the needle, thereby changing the light transmission factor, and the needle can be sucked or attracted substantially in the vertical direction by the electrostatic force in the vertical direction generated by voltage application to the second fixed electrode and the needle, thereby holding the displacement state of the needle or the electrostatic force is canceled and the displacement state can be canceled.
The light modulation element in this invention comprises a needle being partially supported on the side of a substrate and having electric conductivity and a first fixed electrode and a second fixed electrode being placed facing the needle, wherein the needle is displaced substantially vertically with respect to the substrate based on a potential difference caused by voltage application to the first fixed electrode and the needle, thereby changing a light modulation factor and wherein the displacement state of the needle is held or canceled by voltage application to the second fixed electrode and the needle.
In the light modulation element, the needle can be moved substantially in the vertical direction in response to the potential difference by the electrostatic force in the vertical direction generated by voltage application to the first fixed electrode and the needle, thereby changing the light transmission factor, and the needle can be sucked or attracted substantially in the horizontal direction by the electrostatic force in the horizontal direction generated by voltage application to the second fixed electrode and the needle, thereby holding the displacement state of the needle or the electrostatic force is canceled and the displacement state can be canceled.
In the light modulation element in this invention, the needle has a shield property and is placed in an intermediate point on a light path and the light shield amount in the light path is changed by displacement of the needle.
In the light modulation element, the numerical aperture of the light path is changed in response to the displacement amount of the needle having a shield property, placed in an intermediate point on the light path, whereby the light shield amount can be changed.
In the light modulation element in this invention, the light transmission factor of the light modulation element is changed based on any of interference effect, the proximity field optical effect, diffraction effect, or light deflection effect produced as the needle is displaced.
In the light modulation element, the needle is displaced, whereby the light transmission factor can be changed for executing light modulation using the interference effect, such as Fabry-Perot interference, the proximity field optical effect that as a needle moves close to a substrate where light is totally reflected and guided, the light is coupled, the diffraction effect of Bragg diffraction, etc., the light deflection effect of light refraction, or the like.
The light modulation element in this invention comprises a needle partially being supported on a transparent substrate transparent for light to be modulated and having a shield property and electric conductivity, a first fixed electrode being opposed to a first direction of the needle and provided like a wall on a plane perpendicular to the transparent substrate, a second fixed electrode being opposed to a second direction of the needle and provided on a plane parallel to the transparent substrate, and a shield film being formed with an opening left as a light modulation area, wherein the needle is moved in the first direction by an electrostatic force produced by voltage application to the needle and the first fixed electrode, thereby executing light modulation and wherein the needle is sucked or attracted in the second direction by voltage application to the needle and the second fixed electrode for holding the displacement state of the needle or the electrostatic force is canceled for canceling the displacement state.
In the light modulation element, voltage is applied to the needle supported on the transparent substrate and the first fixed electrode opposed to the first direction of the needle, whereby the needle can be displaced in the first direction for executing light modulation, and voltage is applied to the second fixed electrode opposed to the second direction of the needle and the needle, whereby the needle can be sucked or attracted in the second direction for holding the displacement state of the needle or the electrostatic force is canceled and the displacement state can be canceled.
In the light modulation element in this invention, a plurality of the needles and a plurality of the first fixed electrodes are disposed like a grid.
In the light modulation element, a plurality of the needles and a plurality of the first fixed electrodes are disposed like a grid, whereby one pixel area is made up of a plurality of the needles and a plurality of the first fixed electrodes and if an operation failure occurs in any needle, it does not have a large effect on light modulation as the whole of the one pixel area because of presence of another needle, and stable light modulation operation can be performed. The needles and the first fixed electrodes are disposed like a grid, whereby the light modulation element configuration high in space efficiency can be provided.
In this invention, there is provided an array-type light modulation element comprising a plurality of parallel scan signal electrodes, a plurality of image signal electrodes orthogonal to the scan signal electrodes, the elements being placed at intersection points of the scan signal electrodes and the image signal electrodes, characterized in that the displacement state of each needle is held or canceled by a signal of the scan signal electrode and the displacement state of each needle is changed by a signal of the image signal electrode.
In the array-type light modulation element, the needle is displaced by the signal of the image signal electrode for changing the light transmission factor and the displacement state of the needle can be held or canceled by the signal of the scan signal electrode disposed in the direction orthogonal to the image signal electrode; the light modulation state can be provided with a memory property according to a simple configuration without providing the electrode connected separately to each needle. Thus, active matrix drive is enabled.
In this invention, there is provided an array-type light modulation element comprising a plurality of parallel scan signal electrodes, a plurality of latch signal electrodes being placed side by side with the scan signal electrodes, a plurality of image signal electrodes orthogonal to the scan signal electrodes, the latch signal electrodes and light modulation elements, the elements being placed at intersection points of the scan signal electrodes and the latch signal electrodes and the image signal electrodes, characterized in that the displacement state of each needle is held or canceled by signals of the scan signal electrode and the latch signal electrode and the displacement state of each needle is changed by a signal of the image signal electrode.
In the array-type light modulation element, the displacement state of each needle is held or canceled by the signals of the scan signal electrode and the latch signal electrode and the displacement state of each needle can be changed by the signal of the image signal electrode; simply the latch signal electrodes are provided, whereby the light modulation state can be provided with a memory property without changing light modulation control.
In this invention, the light modulation element is in a shield state when the needle does not operate and wherein a light transmission factor increases as the needle is displaced from the shield state by an electrostatic force.
In the array-type light modulation element, the neutral state in which voltage of rightly the same potential is applied to the image signal electrode and the scan signal electrode is adopted as the shield state of the light modulation element, whereby the light modulation element can execute light modulation from the initial shield state to the light passing-through state.
In the array-type light modulation in this invention, the light modulation element is in a light passing-through state when the needle does not operate and wherein a light transmission factor decreases as the needle is displaced by an electrostatic force.
In the array-type light modulation element, the neutral state in which voltage of rightly the same potential is applied to the image signal electrode and the scan signal electrode is adopted as the light passing-through state of the light modulation element, whereby the light modulation element can execute light modulation from the initial light passing-through state to the shield state.
In this invention, there is provided a drive method of an array-type light modulation element, the method comprising the steps of in a write scan period of the light modulation element, canceling holding the needle by a scan signal or a scan signal and a latch signal and displacing the needle to any desired position by an image signal and in a non-write scan period, holding the displacement state of the needle by a scan signal or a scan signal and a latch signal.
In the array-type light modulation element drive method, in the write scan period of the light modulation element, holding the needle is canceled by the scan signal or the scan signal and the latch signal and the needle is displaced to any desired position by the image signal, whereby light modulation can be executed. In the non-write scan period, the needle is held by the scan signal or the scan signal and the latch signal, whereby the displacement state of the needle is held and the light modulation state can be provided with a memory property.
In the array-type light modulation element drive method in this invention, the needle is binary-driven with two positions as displacement destinations.
In the array-type light modulation element drive method, the needle is moved to either of the two different positions in response to the potential difference between the image signal electrode and the needle, whereby the light modulation state can be set selectively between the shield state and the light passing-through state and binary drive is enabled.
In the array-type light modulation element drive method in this invention, the needle is driven for providing multiple levels of gray with any desired positions as displacement destinations.
In the array-type light modulation element drive method, the needle is moved to any desired position in response to the potential difference between the image signal electrode and the needle, whereby an arbitrary light modulation state can be set selectively between the shield state and the light passing-through state and multiple tone drive is enabled.
In the array-type light modulation element drive method in this invention, the move distance of the needle is set in response to a voltage level applied to the image signal.
In the array-type light modulation element drive method, the voltage level applied to the image signal electrode is changed, whereby the needle can be moved to any desired position and modulated light can be changed in analog manner. Thus, multiple tone drive is enabled.
In the array-type light modulation element drive method in this invention, the move distance of the needle is set in response to the voltage application time to the image signal.
In the array-type light modulation element drive method, the voltage application time applied to the image signal electrode is changed, namely, PWM (pulse width modulation), etc., is executed, whereby the needle can be moved to any desired position and modulated light can be changed in analog manner. Thus, multiple tone drive is enabled.
In the array-type light modulation element drive method in this invention, the needle is driven at displacement response speed responsive to the voltage level applied to the image signal.
In the array-type light modulation element drive method, the force of electrostatically sucking the needle is changed in response to the voltage level applied to the image signal electrode in the write scan period, and the needle move distance is changed after the expiration of a given time since holding the needle was released, so that the needle can be moved to any desired position.
In the array-type light modulation element drive method in this invention, the needle is held at a position where the needle is elastically urged at the write scan start time over the light modulation element, wherein holding the needle is canceled after the expiration of an arbitrary time, and wherein the needle is again held at the termination of the write scan.
In the array-type light modulation element drive method, the needle is held at the position where the needle is elastically urged at the write scan start time over the light modulation element, and holding the needle is canceled after the expiration of an arbitrary time, whereby the needle starts to move, and the needle is again held at the termination of the write scan, whereby the needle is held at any desired position, so that the needle can be moved to any desired position.
In the array-type light modulation element drive method in this invention, the period during which the needle is held at the position where the needle is elastically urged is set overlapping a write scan period over another row.
In the array-type light modulation element drive method, the period during which the needle is held at the position where the needle is elastically urged is set overlapping the write scan period over another row, whereby even the light modulation element whose response speed is low can be driven at high speed without wasting the time.
In this invention, there is provided a flat-panel display unit comprising an array-type light modulation element, a surface light source being placed facing the array-type light modulation element, and fluorescent material being placed on an opposite side to the surface light source with the array-type light modulation element between, characterized in that light passing through the array-type light modulation element causes the fluorescent material to emit light for producing display.
According to the configuration, the needle is moved by the electrostatic suction force for changing the light transmission factor of the light modulation element and light emitted from the surface light source via the light modulation element is applied to the fluorescent material, thereby exciting the fluorescent material for emitting light, enabling image display based on image information. Thus, the light from the light source can be applied directly to the fluorescent material for improving the light use efficiency, and the viewing angle can be widened because of the scattering property of the fluorescent material. Since the needle is operated electromechanically, the drive voltage can be lowered and the light modulation state can be held, thus active matrix drive is enabled and high image quality can also be provided in a moving picture. Further, multiple tone drive is also enabled.
In the flat-panel display unit in this invention, the light emitted from the light source is ultraviolet light.
According to the configuration, the display unit with ultraviolet light as a light source can be provided.